> are the solar panels worth the added manufacturing cost and weight? "worth" here implies the third factor that you didn't explicitly mention: how much power

> are the solar panels worth the added manufacturing cost and weight? "worth" here implies the third factor that you didn't explicitly mention: how much power you get off them. And "69 miles per week of charging" is pretty small, hardly worth it unless it's extremely cheap in vehicle cost and weight. You're not wrong with the qualifiers "people using their cars once or twice a week to drive 10km to do groceries" and "some people don't own the land they park their car on" but each qualifier of the prospective customer greatly decreases the potential market size. Combined with a qualifier that they must be without good access to shared transport (so not in a big city, but not on their own land); then you might be looking at corner cases, not a viable market.